Conventionally, a direct-injection type engine (a diesel engine or a spark ignition type engine) provided with a fuel injector for injecting fuel directly into a combustion chamber, in which a fuel injection is performed during the latter half of a compression stroke, is known. In this engine, it is effective to facilitate the mixture of fuel and air in the combustion chamber in order to decrease an amount of discharged emission.
To this end, for example, in a diesel engine described in the Unexamined Japanese Patent Publication No. 7-208173, a land portion (a protruded portion) is provided on a central portion of a bottom surface of a cavity provided in a top portion of a piston and a plurality of convex portions extending in a direction perpendicular to an axis of a fuel spray and a plurality of recessed portions extending in the direction perpendicular to the axis of the fuel spray are formed in a stripe pattern on a top surface of the land portion. Thereby, as shown in FIG. 8, a leading portion of the fuel spray positively impinges on the top surface (the surface having the convex and recessed portions) of the land portion. As a result, the diffusion of the leading portion of the fuel spray is facilitated in all directions and the mixture of the fuel and the air can be facilitated.